The present invention relates generally to the mixing of gas into liquids, and more particularly to a novel method of obtaining such mixing and to an arrangement for carrying out the method.
There are many instances where it is necessary to mix gas or gases into liquids. One of these is the aeration of liquid nutrient media in the growing of microorganisms and, the harvesting of the metabolic products of such microorganisms. Said mixing also is needed e.g. for various chemical gas reactions. There are, in fact, a great number of applications where gas must be as finely dispersed as possible in a liquid. Devices for obtaining such gas dispersions in liquids are already known. For example, it is known to provide a vessel in its interior with a hollow impeller that is mounted for rotation and has located adjacent its axis an inlet formed with a venturi-like constriction. When the impeller rotates the liquid is drawn in through the constriction and is expelled at or near the periphery of the expeller back into the vessel. Outlet openings for gas are provided in the impeller in the region of the throat of the venturi-like constriction so that the suction which results in this region from the flow of liquid is communicated to these outlet openings which in turn communicate with a source of gas, whereby the gas is drawn into the liquid and becomes admixed therewith.
This arrangement has the advantage that the formation of a liquid-gas dispersion is possible without requiring the use of expensive compressors, and that in fact a suction effect is obtained in the throat of the venturi-like constriction. This means that the expenses involved with having to pressurize the gas as in the prior art, are avoided in this arrangement.
However, it has been found that while this device is very advantageous, it is not always suitable in various applications. The efficiency of the device, that is the amount of gas which it is able to introduce into the liquid, is sometimes not adequate for a particular requirement, especially if two or more different gases must be admitted into the liquid which have to be kept separated until they are actually injected into the liquid. Such a requirement exists, for example, when yeast is to be obtained from methane as the carbon source, so that the methane and in addition air must be admitted into liquid. It is known that within a wide range of mixtures a combination of methane and air forms an explosive mix so that a separate admission of methane and air into the liquid is absolutely essential for safety reasons. Evidently, this is not possible with the prior-art device described above. Another drawback of this device is that in many instances the amount of gas that can be admitted into the liquid via the gas outlets that discharge into the throat of the venturi-like constriction, is simply not adequate for a particular requirement.